[PATCH v5 0/2] nfs-utils: signed filehandle support

[PATCH v5 0/2] nfs-utils: signed filehandle support

[Benjamin Coddington]

Here are two patches allowing userspace to set a secret key for kNFSD to
sign filehandles, and also set the option to sign filehandles for an
export.

The secret key passed to the server is the first 128 bits of a sha1 hash of
the contents of a file configured via the nfs.conf server section
"fh_key_file".  Exports that have the option "sign_fh" set will cause the
server to use this key to append an 8-byte siphash of the filehandle onto
each filehandle.

This version of the userspace patches correspond with the v5 of the kernel
changes which have been posted here:
https://lore.kernel.org/linux-nfs/cover.1770660136.git.bcodding@hammerspace.com

This work is based on a branch that includes Jeff Layton's patch for
min-threads:
https://lore.kernel.org/linux-nfs/20260112-minthreads-v1-1-30c5f4113720@kernel.org/

.. and Jeff Layton's v2 series to fix up userspace handling of kernels that
may not support the most recent netlink attributes:
https://lore.kernel.org/linux-nfs/20260204-minthreads-v2-0-a7eba34201e9@kernel.org/

.. and my patch to automatically load required modules:
https://lore.kernel.org/linux-nfs/09076517d782c31cc0a654563b42b78c846c5f38.1770236512.git.bcodding@hammerspace.com

Comments and critique welcomed.

Changes on v5:
	- add -k,--fh-key_file= argument to "nfsdctl threads" command (Jeff Layton)
	- fail if "nfsdctl threads -k" unsuported by kernel (Jeff Layton)

Benjamin Coddington (2):
  exportfs: Add support for export option sign_fh
  nfsdctl/rpc.nfsd: Add support for passing encrypted filehandle key

 nfs.conf                     |  1 +
 support/include/nfs/export.h |  2 +-
 support/include/nfslib.h     |  2 +
 support/nfs/Makefile.am      |  4 +-
 support/nfs/exports.c        |  4 ++
 support/nfs/fh_key_file.c    | 79 ++++++++++++++++++++++++++++++++++++
 systemd/nfs.conf.man         |  1 +
 utils/exportfs/exportfs.c    |  2 +
 utils/exportfs/exports.man   |  9 ++++
 utils/nfsd/nfssvc.h          |  1 +
 utils/nfsdctl/nfsd_netlink.h |  1 +
 utils/nfsdctl/nfsdctl.8      |  8 +++-
 utils/nfsdctl/nfsdctl.c      | 57 +++++++++++++++++++++++---
 13 files changed, 161 insertions(+), 10 deletions(-)
 create mode 100644 support/nfs/fh_key_file.c


base-commit: 8f54511aefe1455161a6c4406ed8c770139f61e3
prerequisite-patch-id: b0d57152c98d360daa9a71e6fa9759b7eb9de348
prerequisite-patch-id: 99680869954aef9f878c24ec9ee1302ab7f24b1a
prerequisite-patch-id: 2ab31271461352d11bcce760e45573f9e6459553
prerequisite-patch-id: 22c392c9dba2e63916af6cd8fbf4e9d6bce9d01c
prerequisite-patch-id: 50f6f48932426f89060eb77de58718baa80b979f
-- 
2.50.1

[PATCH v5 1/2] exportfs: Add support for export option sign_fh

[Benjamin Coddington]

If configured with "sign_fh", exports will be flagged to signal that
filehandles should be signed with a Message Authentication Code (MAC).

Signed-off-by: Benjamin Coddington <bcodding@hammerspace.com>
---
 support/include/nfs/export.h | 2 +-
 support/nfs/exports.c        | 4 ++++
 utils/exportfs/exportfs.c    | 2 ++
 utils/exportfs/exports.man   | 9 +++++++++
 4 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/support/include/nfs/export.h b/support/include/nfs/export.h
index be5867cffc3c..ef3f3e7ea684 100644
--- a/support/include/nfs/export.h
+++ b/support/include/nfs/export.h
@@ -19,7 +19,7 @@
 #define NFSEXP_GATHERED_WRITES	0x0020
 #define NFSEXP_NOREADDIRPLUS	0x0040
 #define NFSEXP_SECURITY_LABEL	0x0080
-/* 0x100 unused */
+#define NFSEXP_SIGN_FH		0x0100
 #define NFSEXP_NOHIDE		0x0200
 #define NFSEXP_NOSUBTREECHECK	0x0400
 #define NFSEXP_NOAUTHNLM	0x0800
diff --git a/support/nfs/exports.c b/support/nfs/exports.c
index 21ec6486ba3d..6b4ca87ee957 100644
--- a/support/nfs/exports.c
+++ b/support/nfs/exports.c
@@ -310,6 +310,8 @@ putexportent(struct exportent *ep)
 		fprintf(fp, "nordirplus,");
 	if (ep->e_flags & NFSEXP_SECURITY_LABEL)
 		fprintf(fp, "security_label,");
+	if (ep->e_flags & NFSEXP_SIGN_FH)
+		fprintf(fp, "sign_fh,");
 	fprintf(fp, "%spnfs,", (ep->e_flags & NFSEXP_PNFS)? "" : "no_");
 	if (ep->e_flags & NFSEXP_FSID) {
 		fprintf(fp, "fsid=%d,", ep->e_fsid);
@@ -676,6 +678,8 @@ parseopts(char *cp, struct exportent *ep, int *had_subtree_opt_ptr)
 			setflags(NFSEXP_NOREADDIRPLUS, active, ep);
 		else if (!strcmp(opt, "security_label"))
 			setflags(NFSEXP_SECURITY_LABEL, active, ep);
+		else if (!strcmp(opt, "sign_fh"))
+			setflags(NFSEXP_SIGN_FH, active, ep);
 		else if (!strcmp(opt, "nohide"))
 			setflags(NFSEXP_NOHIDE, active, ep);
 		else if (!strcmp(opt, "hide"))
diff --git a/utils/exportfs/exportfs.c b/utils/exportfs/exportfs.c
index 748c38e3e966..54ce62c5ce9a 100644
--- a/utils/exportfs/exportfs.c
+++ b/utils/exportfs/exportfs.c
@@ -718,6 +718,8 @@ dump(int verbose, int export_format)
 				c = dumpopt(c, "nordirplus");
 			if (ep->e_flags & NFSEXP_SECURITY_LABEL)
 				c = dumpopt(c, "security_label");
+			if (ep->e_flags & NFSEXP_SIGN_FH)
+				c = dumpopt(c, "sign_fh");
 			if (ep->e_flags & NFSEXP_NOACL)
 				c = dumpopt(c, "no_acl");
 			if (ep->e_flags & NFSEXP_PNFS)
diff --git a/utils/exportfs/exports.man b/utils/exportfs/exports.man
index efbc6ef65c5f..7f0278fb8d33 100644
--- a/utils/exportfs/exports.man
+++ b/utils/exportfs/exports.man
@@ -351,6 +351,15 @@ file.  If you put neither option,
 .B exportfs
 will warn you that the change has occurred.
 
+.TP
+.IR sign_fh
+This option enforces signing filehandles on the export.  If the server has
+been configured with a secret key for such purpose, filehandles will include
+a hash to verify the filehandle was created by the server in order to guard
+against filehandle guessing attacks which can bypass path-name based access
+restrictions.  Note that for NFSv3 some exported filesystems may exceed the
+maximum filehandle size when the signing hash is added.
+
 .TP
 .IR insecure_locks
 .TP
-- 
2.50.1

[PATCH v5 2/2] nfsdctl/rpc.nfsd: Add support for passing encrypted filehandle key

[Benjamin Coddington]

If fh-key-file=<path> is set in the nfsd section of nfs.conf, the "nfsdctl
autostart" command will hash the contents of the file with libuuid's
uuid_generate_sha1 and send the first 16 bytes into the kernel on
NFSD_A_SERVER_FH_KEY. A compatible kernel can use this key to sign
filehandles.

Also add -k, --fh-key-file=<path> option to the "nfsdctl threads" command
effecting the same result.

Signed-off-by: Benjamin Coddington <bcodding@hammerspace.com>
---
 nfs.conf                     |  1 +
 support/include/nfslib.h     |  2 +
 support/nfs/Makefile.am      |  4 +-
 support/nfs/fh_key_file.c    | 79 ++++++++++++++++++++++++++++++++++++
 systemd/nfs.conf.man         |  1 +
 utils/nfsd/nfssvc.h          |  1 +
 utils/nfsdctl/nfsd_netlink.h |  1 +
 utils/nfsdctl/nfsdctl.8      |  8 +++-
 utils/nfsdctl/nfsdctl.c      | 57 +++++++++++++++++++++++---
 9 files changed, 145 insertions(+), 9 deletions(-)
 create mode 100644 support/nfs/fh_key_file.c

diff --git a/nfs.conf b/nfs.conf
index 3cca68c3530d..39068c19d7df 100644
--- a/nfs.conf
+++ b/nfs.conf
@@ -76,6 +76,7 @@
 # vers4.2=y
 rdma=y
 rdma-port=20049
+# fh-key-file=/etc/nfs_fh.key
 
 [statd]
 # debug=0
diff --git a/support/include/nfslib.h b/support/include/nfslib.h
index eff2a486307f..c8601a156cba 100644
--- a/support/include/nfslib.h
+++ b/support/include/nfslib.h
@@ -22,6 +22,7 @@
 #include <paths.h>
 #include <rpcsvc/nfs_prot.h>
 #include <nfs/nfs.h>
+#include <uuid/uuid.h>
 #include "xlog.h"
 
 #ifndef _PATH_EXPORTS
@@ -132,6 +133,7 @@ struct rmtabent *	fgetrmtabent(FILE *fp, int log, long *pos);
 void			fputrmtabent(FILE *fp, struct rmtabent *xep, long *pos);
 void			fendrmtabent(FILE *fp);
 void			frewindrmtabent(FILE *fp);
+int				hash_fh_key_file(const char *fh_key_file, uuid_t hash);
 
 _Bool state_setup_basedir(const char *, const char *);
 int setup_state_path_names(const char *, const char *, const char *, const char *, struct state_paths *);
diff --git a/support/nfs/Makefile.am b/support/nfs/Makefile.am
index 2e1577cc12df..775bccc6c5ea 100644
--- a/support/nfs/Makefile.am
+++ b/support/nfs/Makefile.am
@@ -7,8 +7,8 @@ libnfs_la_SOURCES = exports.c rmtab.c xio.c rpcmisc.c rpcdispatch.c \
 		   xcommon.c wildmat.c mydaemon.c \
 		   rpc_socket.c getport.c \
 		   svc_socket.c cacheio.c closeall.c nfs_mntent.c \
-		   svc_create.c atomicio.c strlcat.c strlcpy.c
-libnfs_la_LIBADD = libnfsconf.la
+		   svc_create.c atomicio.c strlcat.c strlcpy.c fh_key_file.c
+libnfs_la_LIBADD = libnfsconf.la -luuid
 libnfs_la_CPPFLAGS = $(AM_CPPFLAGS) $(CPPFLAGS) -I$(top_srcdir)/support/reexport
 
 libnfsconf_la_SOURCES = conffile.c xlog.c
diff --git a/support/nfs/fh_key_file.c b/support/nfs/fh_key_file.c
new file mode 100644
index 000000000000..ee26df5b70bd
--- /dev/null
+++ b/support/nfs/fh_key_file.c
@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2025 Benjamin Coddington <bcodding@hammerspace.com>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
+ * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
+ * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
+ * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
+ * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/types.h>
+#include <unistd.h>
+#include <errno.h>
+#include <uuid/uuid.h>
+
+#include "nfslib.h"
+
+#define HASH_BLOCKSIZE  256
+int hash_fh_key_file(const char *fh_key_file, uuid_t uuid)
+{
+	const char seed_s[] = "8fc57f1b-1a6f-482f-af92-d2e007c1ae58";
+	FILE *sfile = NULL;
+	char buf[HASH_BLOCKSIZE];
+	size_t pos;
+	int ret = 0;
+
+	sfile = fopen(fh_key_file, "r");
+	if (!sfile) {
+		ret = errno;
+		xlog(L_ERROR, "Unable to read fh-key-file %s: %s", fh_key_file, strerror(errno));
+		goto out;
+	}
+
+	uuid_parse(seed_s, uuid);
+
+	while (1) {
+		size_t sread;
+		pos = 0;
+
+		if (feof(sfile))
+			goto finish_block;
+
+		sread = fread(buf + pos, 1, HASH_BLOCKSIZE - pos, sfile);
+		pos += sread;
+
+		if (pos == HASH_BLOCKSIZE)
+			break;
+
+		if (sread != HASH_BLOCKSIZE) {
+			ret = ferror(sfile);
+			if (ret)
+				goto out;
+			goto finish_block;
+		}
+		uuid_generate_sha1(uuid, uuid, buf, HASH_BLOCKSIZE);
+	}
+finish_block:
+	if (pos)
+		uuid_generate_sha1(uuid, uuid, buf, pos);
+out:
+	if (sfile)
+		fclose(sfile);
+	return ret;
+}
diff --git a/systemd/nfs.conf.man b/systemd/nfs.conf.man
index ecdc4fc90327..a6b5c907b457 100644
--- a/systemd/nfs.conf.man
+++ b/systemd/nfs.conf.man
@@ -176,6 +176,7 @@ Recognized values:
 .BR vers4.1 ,
 .BR vers4.2 ,
 .BR rdma ,
+.BR fh-key-file ,
 
 Version and protocol values are Boolean values as described above,
 and are also used by
diff --git a/utils/nfsd/nfssvc.h b/utils/nfsd/nfssvc.h
index 4d53af1a8bc3..463110cac804 100644
--- a/utils/nfsd/nfssvc.h
+++ b/utils/nfsd/nfssvc.h
@@ -30,3 +30,4 @@ void	nfssvc_setvers(unsigned int ctlbits, unsigned int minorvers4,
 		       unsigned int minorvers4set, int force4dot0);
 int	nfssvc_threads(int nrservs);
 void	nfssvc_get_minormask(unsigned int *mask);
+int nfssvc_setfh_key(const char *fh_key_file);
diff --git a/utils/nfsdctl/nfsd_netlink.h b/utils/nfsdctl/nfsd_netlink.h
index e9efbc9e63d8..97c7447f4d14 100644
--- a/utils/nfsdctl/nfsd_netlink.h
+++ b/utils/nfsdctl/nfsd_netlink.h
@@ -36,6 +36,7 @@ enum {
 	NFSD_A_SERVER_LEASETIME,
 	NFSD_A_SERVER_SCOPE,
 	NFSD_A_SERVER_MIN_THREADS,
+	NFSD_A_SERVER_FH_KEY,
 
 	__NFSD_A_SERVER_MAX,
 	NFSD_A_SERVER_MAX = (__NFSD_A_SERVER_MAX - 1)
diff --git a/utils/nfsdctl/nfsdctl.8 b/utils/nfsdctl/nfsdctl.8
index a86ffe8e1f4d..1f526e77bebf 100644
--- a/utils/nfsdctl/nfsdctl.8
+++ b/utils/nfsdctl/nfsdctl.8
@@ -159,6 +159,12 @@ These options are specific to the "threads" subcommand:
     kernel will start the minimum number and dynamically start and stop threads as
     needed. If the minimum is larger than the maximum, then dynamic threadis is
     disabled, and the maximum number is started.
+
+\-k, \-\-fh\-key\-file=
+    If set to the path of a file, use the first 128 bits of the sha1 hash
+    of the file's contents as the server's filehandle signing key.
+    Exports with the "sign_fh" export option will use this key to append an
+    a signature to guard against filehandle guessing attacks.
 .fam
 .fi
 .if n .RE
@@ -336,4 +342,4 @@ privileges.
 nfs.conf(5), rpc.nfsd(8), rpc.mountd(8), exports(5), exportfs(8), rpc.rquotad(8), nfsstat(8), netconfig(5)
 .SH "AUTHOR"
 .sp
-Jeff Layton
\ No newline at end of file
+Jeff Layton
diff --git a/utils/nfsdctl/nfsdctl.c b/utils/nfsdctl/nfsdctl.c
index 6a20d180a81e..ed0c4fded339 100644
--- a/utils/nfsdctl/nfsdctl.c
+++ b/utils/nfsdctl/nfsdctl.c
@@ -29,6 +29,7 @@
 
 #include <readline/readline.h>
 #include <readline/history.h>
+#include <uuid/uuid.h>
 
 #ifdef USE_SYSTEM_NFSD_NETLINK_H
 #include <linux/nfsd_netlink.h>
@@ -42,6 +43,7 @@
 #include "lockd_netlink.h"
 #endif
 
+#include "nfslib.h"
 #include "nfsdctl.h"
 #include "conffile.h"
 #include "xlog.h"
@@ -636,8 +638,10 @@ out:
 }
 
 static int threads_doit(struct nl_sock *sock, int cmd, int grace, int lease,
-			int pool_count, int *pool_threads, char *scope, int minthreads)
+			int pool_count, int *pool_threads, char *scope, int minthreads,
+			uuid_t fh_key)
 {
+	struct nl_data *fh_key_data = NULL;
 	struct genlmsghdr *ghdr;
 	struct nlmsghdr *nlh;
 	struct nl_msg *msg;
@@ -663,6 +667,19 @@ static int threads_doit(struct nl_sock *sock, int cmd, int grace, int lease,
 			nla_put_string(msg, NFSD_A_SERVER_SCOPE, scope);
 		if (minthreads >= 0)
 			nla_put_u32(msg, NFSD_A_SERVER_MIN_THREADS, minthreads);
+		if (!uuid_is_null(fh_key)) {
+			if (nfsd_threads_max_nlattr < NFSD_A_SERVER_FH_KEY) {
+				xlog(L_ERROR, "This kernel does not support signed filehandles.");
+			} else {
+				fh_key_data = nl_data_alloc(fh_key, sizeof(uuid_t));
+				if (!fh_key_data) {
+					xlog(L_ERROR, "failed to allocate netlink data");
+					ret = 1;
+					goto out;
+				}
+				nla_put_data(msg, NFSD_A_SERVER_FH_KEY, fh_key_data);
+			}
+		}
 		for (i = 0; i < pool_count; ++i)
 			nla_put_u32(msg, NFSD_A_SERVER_THREADS, pool_threads[i]);
 	}
@@ -697,14 +714,17 @@ static int threads_doit(struct nl_sock *sock, int cmd, int grace, int lease,
 out_cb:
 	nl_cb_put(cb);
 out:
+	if (fh_key_data)
+		nl_data_free(fh_key_data);
 	nlmsg_free(msg);
 	return ret;
 }
 
 static void threads_usage(void)
 {
-	printf("Usage: %s threads { --min-threads=X } [ pool0_count ] [ pool1_count ] ...\n", taskname);
+	printf("Usage: %s threads { --min-threads=X } { --fh-key-file=file } [ pool0_count ] [ pool1_count ] ...\n", taskname);
 	printf("    --min-threads= set the minimum thread count per pool to value\n");
+	printf("    --fh-key-file= path to a file to set the filehandle signing key\n");
 	printf("    pool0_count: thread count for pool0, etc...\n");
 	printf("Omit any arguments to show current thread counts.\n");
 }
@@ -712,6 +732,7 @@ static void threads_usage(void)
 static const struct option threads_options[] = {
 	{ "help", no_argument, NULL, 'h' },
 	{ "min-threads", required_argument, NULL, 'm' },
+	{ "fh-key-file", required_argument, NULL, 'k' },
 	{ },
 };
 
@@ -721,9 +742,11 @@ static int threads_func(struct nl_sock *sock, int argc, char **argv)
 	int *pool_threads = NULL;
 	int minthreads = -1;
 	int opt, pools = 0;
+	uuid_t fh_key;
 
+	uuid_clear(fh_key);
 	optind = 1;
-	while ((opt = getopt_long(argc, argv, "hm:", threads_options, NULL)) != -1) {
+	while ((opt = getopt_long(argc, argv, "hm:k:", threads_options, NULL)) != -1) {
 		switch (opt) {
 		case 'h':
 			threads_usage();
@@ -741,6 +764,18 @@ static int threads_func(struct nl_sock *sock, int argc, char **argv)
 				return 1;
 			}
 			break;
+		case 'k':
+			if (nfsd_threads_max_nlattr < NFSD_A_SERVER_FH_KEY) {
+				xlog(L_ERROR, "This kernel does not support signed filehandles.\n");
+				return 1;
+			}
+
+			errno = hash_fh_key_file(optarg, fh_key);
+			if (errno) {
+				fprintf(stderr, "Error hashing key file %s: %s.", optarg, strerror(errno));
+				return 1;
+			}
+			break;
 		}
 	}
 
@@ -768,7 +803,8 @@ static int threads_func(struct nl_sock *sock, int argc, char **argv)
 			}
 		}
 	}
-	return threads_doit(sock, cmd, 0, 0, pools, pool_threads, NULL, minthreads);
+	return threads_doit(sock, cmd, 0, 0, pools, pool_threads, NULL,
+				minthreads, fh_key);
 }
 
 /*
@@ -1760,8 +1796,9 @@ static int autostart_func(struct nl_sock *sock, int argc, char ** argv)
 	int *threads, grace, lease, idx, ret, opt, pools, minthreads;
 	struct conf_list *thread_str;
 	struct conf_list_node *n;
-	char *scope, *pool_mode;
+	char *scope, *pool_mode, *fh_key_file;
 	bool failed_listeners = false;
+	uuid_t fh_key;
 
 	optind = 1;
 	while ((opt = getopt_long(argc, argv, "h", help_only_options, NULL)) != -1) {
@@ -1836,6 +1873,14 @@ static int autostart_func(struct nl_sock *sock, int argc, char ** argv)
 		threads[0] = DEFAULT_AUTOSTART_THREADS;
 	}
 
+	uuid_clear(fh_key);
+	fh_key_file = conf_get_str("nfsd", "fh-key-file");
+	if (fh_key_file) {
+		ret = hash_fh_key_file(fh_key_file, fh_key);
+		if (ret)
+			return ret;
+	}
+
 	lease = conf_get_num("nfsd", "lease-time", 0);
 	scope = conf_get_str("nfsd", "scope");
 	minthreads = conf_get_num("nfsd", "min-threads", -1);
@@ -1846,7 +1891,7 @@ static int autostart_func(struct nl_sock *sock, int argc, char ** argv)
 	}
 
 	ret = threads_doit(sock, NFSD_CMD_THREADS_SET, grace, lease, pools,
-			   threads, scope, minthreads);
+			   threads, scope, minthreads, fh_key);
 out:
 	free(threads);
 	return ret;
-- 
2.50.1